FinFET with Embedded MOS Varactor and Method of Making Same

ABSTRACT

Embodiments of the present disclosure are a semiconductor device, a FinFET device, and a method of forming a FinFET device. An embodiment is semiconductor device including a first FinFET over a substrate, wherein the first FinFET includes a first set of semiconductor fins. The semiconductor device further includes a first body contact for the first FinFET over the substrate, wherein the first body contact includes a second set of semiconductor fins, and wherein the first body contact is laterally adjacent the first FinFET.

BACKGROUND

Transistors are key components of modern integrated circuits. To satisfythe requirements of increasingly faster speed, the drive currents oftransistors need to be increasingly greater. Since the drive currents oftransistors are proportional to gate widths of the transistors,transistors with greater widths are preferred. The increase in gatewidths, however, conflicts with the requirements of reducing the sizesof semiconductor devices. Fin field-effect transistors (FinFET) werethus developed.

In state-of-the-art circuits, the operational frequency of theintegrated circuit is in the order of several hundreds of mega-hertz(MHz) to several giga-hertz (GHz). In such circuits, the rising time ofclock signals is very short, so that voltage fluctuations in the supplyline can be very large. Undesired voltage fluctuations in the powersupply line powering a circuit can cause noise on its internal signalsand degrade noise margins. The degradation of noise margins can reducecircuit reliability or even cause circuit malfunction.

To reduce the magnitude of voltage fluctuations in the power supplylines, filtering, or decoupling capacitors may be used. Decouplingcapacitors act as charge reservoirs that additionally supply currents tocircuits when required to prevent momentary drops in supply voltage.

In an attempt to incorporate the decoupling capacitor with the othercircuitry, the decoupling capacitor has been placed on-chip. One attemptat using an on-chip decoupling capacitor utilizes a thin-film planarcapacitor. These capacitors, however, generally require large areas andare difficult to design and fabricate such that the capacitors have asufficiently large enough capacitance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 5B illustrate in cross-sectional and top down viewsvarious stages in the manufacture of a FinFET device structure accordingto an embodiment;

FIGS. 6A and 6B illustrate schematic representations of a PMOSconfiguration and an NMOS configuration, respectively, of the FinFETdevice illustrated in FIG. 5A;

FIG. 7 illustrates in top-down view a FinFET device with an embeddedvaractor according to another embodiment; and

FIGS. 8A and 8B illustrate schematic representations of a PMOSconfiguration and an NMOS configuration, respectively, of the FinFETdevice illustrated in FIG. 7.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Reference will now be made in detail to embodiments illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts. In the drawings, the shape and thickness may be exaggerated forclarity and convenience. This description will be directed in particularto elements forming part of, or cooperating more directly with, methodsand apparatus in accordance with the present disclosure. It is to beunderstood that elements not specifically shown or described may takevarious forms well known to those skilled in the art. Many alternativesand modifications will be apparent to those skilled in the art, onceinformed by the present disclosure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. It shouldbe appreciated that the following figures are not drawn to scale;rather, these figures are merely intended for illustration.

Embodiments will be described with respect to a specific context, namelya FinFET device with a body contact. Other embodiments may also beapplied, however, to other devices with a FinFET structure with anembedded varactor.

FIG. 1 illustrates a cross-sectional view of a FinFET device 100 at anintermediate stage of processing. The FinFET device 100 includes asemiconductor layer 22 on a semiconductor substrate 20. Thesemiconductor substrate 20 may comprise bulk silicon, doped or undoped,or an active layer of a silicon-on-insulator (SOI) substrate. Generally,an SOI substrate comprises a layer of a semiconductor material such assilicon, germanium, silicon germanium, SOI, silicon germanium oninsulator (SGOI), or combinations thereof. Other substrates that may beused include multi-layered substrates, gradient substrates, or hybridorientation substrates.

The semiconductor substrate 20 may include active devices (not shown inFIG. 1 for clarity). As one of ordinary skill in the art will recognize,a wide variety of devices such as transistors, capacitors, resistors,combinations of these, and the like may be used to generate thestructural and functional requirements of the design for the FinFETdevice 100. The devices may be formed using any suitable methods. Theactive FinFETs 28 may be electrically coupled to the active and passivedevices. Only a portion of the semiconductor substrate 20 is illustratedin the figures, as this is sufficient to fully describe the illustrativeembodiments.

The semiconductor layer 22 may be formed of semiconductor material suchas silicon, germanium, silicon germanium, or the like. In an embodiment,the semiconductor layer 22 is silicon. The semiconductor layer 22 maythen doped through an implantation process to introduce p-type or n-typeimpurities into the semiconductor layer 22.

In FIGS. 2A and 2B, the patterning of the semiconductor layer 22 intothe active fins 24 and the body contact fins 26 is illustrated. FIG. 2Ais a top-down view of FinFET device 100 and FIG. 2B is a cross-sectionalview along line 2B in FIG. 2A. The fin patterning process may beaccomplished by depositing mask material (not shown) such as photoresistor silicon oxide over the semiconductor layer 22. The mask material isthen patterned and the semiconductor layer 22 is etched in accordancewith the pattern. The resulting structure includes a plurality of activefins 24 and body contact fins 26 formed in the semiconductor layer 22.Each fin of the plurality of active fins 24 and body contact fins 26 hasa sidewall being substantially orthogonal to a top surface of thesemiconductor substrate 20. In some embodiments, the semiconductor layer22 is etched to a specific depth, meaning the active fins 24 and thebody contact fins 26 are formed to a height, the active fins 24 heighth₂ from about 10 nm to about 500 nm and the body contact fins 26 heighth₁ from about 10 nm to 500 nm. In one specific embodiment, the activefins 24 are formed to a height h₂ of about 110 nm and the body contactfins 26 are formed to a height h₁ of about 110 nm. The active fins 24may have a width w₂ from about 5 nm to 50 nm and the body contact fins26 may have a width w₁ from about 5 nm to 50 nm. As shown in FIG. 3 a,the active fins 24 may have a length L₁ from about 0.01 um to 10 um andthe body contact fins 26 may have a length L₁ from about 0.1 um to 10um. In an alternative embodiment, active fins 24 and body contact fins26 may be epitaxially grown from a top surface of the semiconductorsubstrate 20 within trenches or openings formed in a patterned layeratop the semiconductor substrate 20. Because the process is known in theart, the details are not repeated herein.

The active fins 24 serve as the fin structure for the to-be-formedFinFETs 28 and the body contact fins 26 serve as the fin structure forthe body contacts 30. Each FinFET 28 may comprise a single active fin 24to as many active fins 24 as necessary for the FinFET device 100. FIGS.1 through 5B illustrate the formation of two FinFETs 28, each with fouractive fins 24 as a non-limiting illustrative embodiment. Similarly, thebody contacts 30 may comprise a single body contact fin 26 to as manybody contact fins 26 as necessary for the FinFET device 100 rather thanthe three body contact fins 26 illustrated in FIGS. 2A through 5B.

Referring now to FIGS. 3A and 3B, a dielectric layer 32 is blanketdeposited on the FinFET device 100. The dielectric layer 32 may be madeof one or more suitable dielectric materials such as silicon oxide,silicon nitride, low-k dielectrics such as carbon doped oxides,extremely low-k dielectrics such as porous carbon doped silicon dioxide,a polymer such as polyimide, combinations of these, or the like. Thedielectric layer 32 may be deposited through a process such as chemicalvapor deposition (CVD), or a spin-on-glass process, although anyacceptable process may be utilized.

FIGS. 4A and 4B illustrate the next step in the manufacturing process,wherein the dielectric layer 32 is thinned to below the level of thetops of the active fins 24 and the tops of the body contact fins 26. Thedielectric layer 32 may be thinned back in a variety of ways. In oneembodiment, this is a multi-step process with the first step involving achemical mechanical polishing (CMP), in which the dielectric layer 32 isreacted and then ground away using an abrasive. This process maycontinue until the tops of the active fins 24 and the body contact fins26 are exposed. The next step of thinning the dielectric layer 32 belowthe tops of the active fins 24 and body contact fins 26 may be performedin a variety of ways. One such way is by a diluted hydrofluoric acid(DHF) treatment or a vapor hydrofluoric acid (VHF) treatment for asuitable time. In another embodiment, the CMP process step may beskipped and the dielectric layer 32 may be selectively thinned backwithout removing the active fins 24 and the body contact fins 26. Thisselective thinning may be performed by the DHF treatment or the VHFtreatment described above.

FIGS. 5A and 5B illustrate the formation of the active gates 38 over theactive fins 24, the dummy gates 34 over the ends of the active fins 24and the body contact fins 26, and the dummy gates 36 over the bodycontact fins 26. The width and length of the dummy gates 34 and 36 maybe different than the active gates 38 (see FIG. 5A), or the dummy gates34 and 36 may have a same width and length as the active gates 38. Theactive gates 38 and the dummy gates 34 and 36 may include a gatedielectric layer (not shown), a gate electrode (not shown), and gatespacers (not shown). The gate dielectric layer may be formed by thermaloxidation, CVD, sputtering, or any other methods known and used in theart for forming a gate dielectric. In other embodiments, the gatedielectric layer includes dielectric materials having a high dielectricconstant (k value), for example, greater than 3.9. The materials mayinclude silicon nitrides, oxynitrides, metal oxides such as HfO₂,HfZrO_(x), HfSiO_(x), HfTiO_(x), HfAlO_(x), the like, or combinationsand multi-layers thereof.

The gate electrode layer may be formed over the gate dielectric layer.The gate electrode layer may comprise a conductive material and may beselected from a group comprising polycrystalline-silicon (poly-Si),poly-crystalline silicon-germanium (poly-SiGe), metallic nitrides,metallic silicides, metallic oxides, and metals. The gate electrodelayer may be deposited by CVD, sputter deposition, or other techniquesknown and used in the art for depositing conductive materials. The topsurface of the gate electrode layer usually has a non-planar topsurface, and may be planarized prior to patterning of the gate electrodelayer or gate etch. Ions may or may not be introduced into the gateelectrode layer at this point. Ions may be introduced, for example, byion implantation techniques. The gate electrode layer and the gatedielectric layer may be patterned to form the active gates 38 and thedummy gates 34 and 36. The gate patterning process may be accomplishedby depositing mask material (not shown) such as photoresist or siliconoxide over the gate electrode layer. The mask material is then patternedand the gate electrode layer is etched in accordance with the pattern.

After the formation of the active gates 38 and the dummy gates 34 and36, source regions 40 and the drain regions 42 may be formed on theactive fins 24. The source regions 40 and the drain regions 42 may bedoped by performing implanting process to implant appropriate dopants tocomplement the dopants in the active fins 24. In another embodiment, thesource regions 40 and the drain regions 42 may be formed by formingrecesses (not shown) in active fins 24 and epitaxially growing materialin the recesses. The source regions 40 and the drain regions 42 may bedoped either through an implantation method as discussed above, or elseby in-situ doping as the material is grown. The dummy gates 34 over theends of the active fins 24 and the body contact fins 26 may be used tocontrol the epitaxial growth of the source regions 40 and the drainregions 42 as well as the body contacts 44. In an embodiment, acontinuous metal layer may overly the four active fins 24 in each of thesource regions 40 to form three source regions 40 in each FinFET 28.Further, a continuous metal layer may overly the four active fins 24 ineach of the drain regions 42 in each of the drain regions 42 to form twodrain regions in each of the FinFETs 28.

In the embodiment illustrated in FIGS. 5A and 5B, the FinFETs 28 may beconfigured in a PMOS or an NMOS configuration. In a PMOS configuration,the active fins 24 may be doped with n-type dopants, the body contactfins 26 may be doped with n-type dopants, the source regions 40 and thedrain regions 42 may be doped with p-type dopants, and the body contacts44 may be doped with n-type dopants. In an NMOS configuration, theactive fins 24 may be doped with p-type dopants, the body contact fins26 may be doped with p-type dopants, the source regions 40 and the drainregions 42 may be doped with n-type dopants, and the body contacts 44may be doped with p-type dopants.

Gate spacers may be formed on opposite sides of the active gates 38 andthe dummy gates 34 and 36. The gate spacers (not shown) are typicallyformed by blanket depositing a spacer layer (not shown) on thepreviously formed structure. The spacer layer may comprise SiN,oxynitride, SiC, SiON, oxide, and the like and may be formed by methodsutilized to form such a layer, such as CVD, plasma enhanced CVD,sputter, and other methods known in the art. The gate spacers are thenpatterned, preferably by anisotropically etching to remove the spacerlayer from the horizontal surfaces of the structure.

In another embodiment, the source regions 40 and the drain regions 42may comprise a lightly doped region and a heavily doped region. In thisembodiment, before the gate spacers are formed, the source regions 40and the drain regions 42 may be lightly doped. After the gate spacersare formed, the source regions 40 and the drain regions 42 may then beheavily doped. This forms lightly doped regions and heavily dopedregions. The lightly doped regions are primarily underneath the gatespacers while the heavily doped regions are outside of the gate spacersalong the active fins 24.

FIGS. 6A and 6B illustrate schematic symbols for a PMOS configurationand an NMOS configuration, respectively, for the FinFETs 28 as shown inFIGS. 5A and 5B. Both of the schematic symbols illustrate the activegate 38 connected to the gate terminal, the source region 40 connectedto the source terminal, the drain region 42 connected to the drainterminal, and the body contact 44 connected to the body terminal.

FIG. 7 illustrates another embodiment of FinFET device 100 wherein thebody contact fins 26 have active gates 46 formed over them. The widthand length of the active gates 46 may be different than the active gates38, or the active gates 46 may have a same width and length as theactive gates 38 (see FIG. 7). The active gates 46 over the body contactfins 26 may form an embedded MOS varactor 50 which may act as adecoupling capacitor. In an embodiment where the embedded MOS varactor50 is configured to act as a decoupling capacitor, the active gates 46may be connected to a bias node, which may vary the capacitance of theembedded MOS varactor 50. Additionally, in an NMOS configuration of theembedded MOS varactor 50, the active gates 46 may be connected to aground node to act as a decoupling capacitor. In a PMOS configuration ofthe embedded MOS varactor 50, the active gates 46 may be connected to apower node to act as a decoupling capacitor.

In the embodiment illustrated in FIG. 7, the FinFETs 28 and the embeddedMOS varactors 50 may each be configured in a PMOS or an NMOSconfiguration. In an embodiment wherein the FinFETs 28 are PMOS and theembedded MOS varactors 50 are NMOS, the active fins 24 may be doped withn-type dopants, the body contact fins 26 may be doped with n-typedopants, the source regions 40 and the drain regions 42 may be dopedwith p-type dopants, and the body contacts 48 may be doped with n-typedopants. In another embodiment wherein the FinFETs 28 are NMOS and theembedded MOS varactors 50 are PMOS, the active fins 24 may be doped withp-type dopants, the body contact fins 26 may be doped with p-typedopants, the source regions 40 and the drain regions 42 may be dopedwith n-type dopants, and the body contacts 44 may be doped with p-typedopants.

FIGS. 8A and 8B illustrate schematic symbols for PMOS and NMOSconfigurations for the FinFETs 28 and embedded MOS varactors 50 as shownin FIG. 7. In FIG. 8A, the FinFET 28 is PMOS and the embedded MOSvaractor 50 is NMOS. In FIG. 8B, the FinFET 28 is NMOS and the embeddedMOS varactor 50 is PMOS. Both of the schematic symbols illustrate theactive gate 38 connected to the gate terminal of the FinFETs 28, thesource region 40 connected to the source terminal of the FinFETs 28, thedrain region 42 connected to the drain terminal of the FinFETs 28, andthe body contact 48 connected to the body terminal of the FinFETs 28. Inan embodiment wherein the FinFET 28 is PMOS and the embedded MOSvaractor 50 is NMOS (see FIG. 8A), the active gates 46 may be connectedto a bias node or a ground node to form a decoupling capacitor. Inanother embodiment wherein the FinFET 28 is NMOS and the embedded MOSvaractor 50 is PMOS (see FIG. 8B), the active gates 46 may be connectedto a bias node or a power node to form a decoupling capacitor.

By replacing the dummy gates 36 with active gates 46 over the bodycontact fins 26 to form embedded MOS varactors 50, the cost of theFinFET device 100 is reduced because the material for the active gates46 may be utilized, for example, as decoupling capacitors. Additionally,the total area of the FinFET device 100 may be reduced by embeddingnecessary capacitors into the already existing structure of the bodycontact fins 26 and the gates over the body contact fins.

An embodiment is semiconductor device comprising a first FinFET over asubstrate, wherein the first FinFET comprises a first set ofsemiconductor fins. The semiconductor device further comprises a firstbody contact for the first FinFET over the substrate, wherein the firstbody contact comprises a second set of semiconductor fins, and whereinthe first body contact is laterally adjacent the first FinFET.

Another embodiment is a FinFET device comprising a first FinFET over asubstrate, the first FinFET comprising a first plurality of fins, and atleast two active gates over the first plurality of fins. The FinFETdevice further comprises a first body contact for the first FinFET overthe substrate, the first body contact comprising a second plurality offins, and at least two active gates over the second plurality of fins.

Yet another embodiment is a method for forming a FinFET device, themethod comprising forming a first FinFET comprising forming a firstplurality of fins over a substrate, forming at least two active gatesover the first plurality of fins, and forming at least two sourceregions and at least two drain regions in the first plurality of fins.The method further comprises forming a first body contact for the firstFinFET comprising forming a second plurality of fins over the substrateforming at least two dummy gates over the second plurality of fins, andforming at least two body contact regions in the second plurality offins.

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions, and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods, and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A semiconductor device comprising: a first FinFETover a substrate, wherein the first FinFET comprises a first set ofsemiconductor fins; and a first body contact for the first FinFET overthe substrate, wherein the first body contact comprises a second set ofsemiconductor fins, and wherein the first body contact is laterallyadjacent the first FinFET.
 2. The semiconductor device of claim 1,wherein the first set of semiconductor fins comprises at least twosemiconductor fins, and wherein the second set of semiconductor finscomprises at least two semiconductor fins.
 3. The semiconductor deviceof claim 1, wherein the first set of semiconductor fins is parallel tothe second set of semiconductor fins.
 4. The semiconductor device ofclaim 1, wherein the first FinFET further comprises at least one activegate having a first width and a first length over the first set ofsemiconductor fins and at least one dummy gate over the first set ofsemiconductor fins, and wherein the first body contact further comprisesat least one dummy gate having a second width and a second length overthe second set of semiconductor fins.
 5. The semiconductor device ofclaim 4, wherein the first width is equal to the second width and thefirst length is equal to the second length.
 6. The semiconductor deviceof claim 1, wherein the first FinFET further comprises at least twosource regions and at least two drain regions, wherein the source anddrain regions are separated by an active gate.
 7. The semiconductordevice of claim 1 further comprising: a second FinFET over thesubstrate, wherein the second FinFET comprises a third set ofsemiconductor fins, and wherein the second FinFET is laterally adjacentthe first FinFET in a direction opposite the first body contact; and asecond body contact for the second FinFET over the substrate, whereinthe second body contact comprises a fourth set of semiconductor fins,wherein the second body contact is laterally adjacent the second FinFETin a direction opposite of the first FinFET.
 8. The semiconductor deviceof claim 1, wherein the first set of fins have a same width and a samelength as the second set of fins.
 9. A FinFET device comprising: a firstFinFET over a substrate, the first FinFET comprising: a first pluralityof fins; and at least two active gates over the first plurality of fins;and a first body contact for the first FinFET over the substrate, thefirst body contact comprising: a second plurality of fins; and at leasttwo active gates over the second plurality of fins.
 10. The FinFETdevice of claim 9, wherein the at least two active gates over the secondplurality of fins forms a MOS varactor.
 11. The FinFET device of claim9, wherein the first FinFET further comprises at least two dummy gatesover the first plurality of fins, and wherein the first body contactfurther comprises at least two dummy gates over the second plurality offins.
 12. The FinFET device of claim 9, wherein the first FinFET has asame number of active gates as the first body contact.
 13. The FinFETdevice of claim 12, wherein the active gates of the first FinFET arelaterally adjacent and aligned with the active gates of the first bodycontact.
 14. The FinFET device of claim 9, wherein the at least twoactive gates of the first body contact are electrically coupled to abias node thereby forming a decoupling capacitor.
 15. The FinFET deviceof claim 9, wherein the at least two active gates of the first bodycontact are electrically coupled to a ground node or a power nodethereby forming a decoupling capacitor.
 16. The FinFET device of claim 9further comprising: a second FinFET over the substrate, the first FinFETcomprising: a third plurality of fins; and at least two active gatesover the third plurality of fins; and a second body contact for thesecond FinFET over the substrate, the second body contact comprising: afourth plurality of fins; and at least two active gates over the fourthplurality of fins, wherein the first plurality, the second plurality,the third plurality, and the fourth plurality of fins are parallel toeach other.
 17. A method for forming a FinFET device, the methodcomprising: forming a first FinFET comprising: forming a first pluralityof fins over a substrate; forming at least two active gates over thefirst plurality of fins; and forming at least two source regions and atleast two drain regions in the first plurality of fins; and forming afirst body contact for the first FinFET comprising: forming a secondplurality of fins over the substrate; forming at least two dummy gatesover the second plurality of fins; and forming at least two body contactregions in the second plurality of fins.
 18. The method of claim 17further comprising forming a first MOS varactor comprising forming atleast two active gates over the second plurality of fins.
 19. The methodof claim 18 further comprising forming a decoupling capacitor comprisingelectrically coupling the at least two active gates over the secondplurality of fins to a bias node.
 20. The method of claim 17 furthercomprising: forming a second FinFET comprising: forming a thirdplurality of fins over the substrate; forming at least two active gatesover the third plurality of fins; and forming at least two sourceregions and at least two drain regions in the third plurality of fins;and forming a second body contact for the second FinFET comprising:forming a fourth plurality of fins over the substrate; forming at leasttwo dummy gates over the fourth plurality of fins; and forming at leasttwo body contact regions in the fourth plurality of fins.